Variation of the mangrove sediment microbiomes and their phenanthrene biodegradation rates during the dry and wet seasons.

Mangrove sediment is a major sink for phenanthrene in natural environments. Consequently, this study investigated the effects of seasonal variation on the biodegradation rates of low (150 mg kg-1), moderate (600 mg kg-1), and high (1200 mg kg-1) phenanthrene-contaminated mangrove sediments using a microcosm study and identified potential key phenanthrene-degrading bacteria using high throughput sequencing of 16 S rRNA gene and quantitative-PCR of the PAH-ring hydroxylating dioxygenase (PAH-RHDα) genes. The biodegradation rates of phenanthrene in all treatments were higher in the wet-season sediments (11.58, 14.51, and 8.94 mg kg-1 sediment day-1) than in the dry-season sediments (3.51, 12.56, and 5.91 mg kg-1 sediment day-1) possibly due to higher nutrient accumulation caused by rainfall and higher diversity of potential phenanthrene-degrading bacteria. The results suggested that the mangrove sediment microbiome significantly clustered according to season. Although Gram-negative phenanthrene-degrading bacteria (i.e., Anaerolineaceae, Marinobacter, and Rhodobacteraceae) played a key role in both dry and wet seasons, distinctly different phenanthrene-degrading bacterial taxa were observed in each season. Halomonas and Porticoccus were potentially responsible for the degradation of phenanthrene in the dry and wet seasons, respectively. The knowledge gained from this study contributes to the development of effective and rationally designed microbiome innovations for oil removal.